Bone and Joint Infections

Historically, bone and joint infections have been described in grim terms. Aids to Surgery, written in 1919, notes that “acute infective osteomyelitis ... is a very fatal disease.” With septic arthritis, “the patient becomes exhausted from toxaemia or pyemia,” and “ankylosis is the usual most favourable termination.” Advances in diagnostic methods, antibiotic therapy, and surgical techniques have resulted in better patient outcomes. In the case of osteomyelitis, treatment with antibiotics and limb salvage protocols is successful in more than 90% of patients with chronic osteomyelitis despite the increase in the number of patients with multiple comorbidities that affect wound healing. However, new challenges are being unveiled. The types of infections that are encountered today are evolving. Host immunity is decreased in many populations, leading to the complexity of the management of bone and joint infections that has never before been encountered. Emergency physicians must consider many subsets of patients who are at increased risk of infection, including injection drug users, patients with acquired immunodeficiency syndrome (AIDS), postsurgical patients, and patients with iatrogenic immune suppression. The emphasis of modern management of bone and joint infections has shifted from prevention of sepsis and death to prompt diagnosis, initiation of treatment, and avoidance of the complications and morbidity associated with chronic bone or joint infections. The overall occurrence of bone and joint infections appears to have remained constant during the past three decades. The incidence of bone infections in hospitalized patients is approximately 1%. In the United States, the incidence of osteomyelitis in children younger than 13 years is 1 in 5000, whereas the incidence of septic arthritis ranges from 5.5 to 12 per 100,000 individuals. Globally, epidemiologic data for community-acquired bone and joint infections in adults vary significantly, with an overall higher incidence in patients of a lower socioeconomic class in developing countries. However, in the United States, there is no correlation between socioeconomic factors or race and the incidence of bone and joint infections. Both bone and joint infections show a bimodal age distribution, occurring most commonly in people younger than 20 years or older than 50 years. In children, bone and joint infections usually occur in previously healthy individuals, and boys have a slightly increased susceptibility to bone infections. In adults, risk factors can usually be identified in patients who present with either bone or joint infection. Orthopedic infections can be classified according to the site of involvement and include osseous (osteomyelitis), articular (septic or suppurative arthritis), bursal (septic bursitis), subcutaneous (cellulitis or abscess), muscular (infectious myositis or abscess), and tendinous (infectious tendinitis or tenosynovitis) varieties. The word osteomyelitis literally means inflammation of the marrow of the bone, but the term is loosely used to refer to infection in any part of the bone. Infectious processes can also be categorized by their onset and are generally designated acute, subacute, or chronic. An acute infection is one that lasts less than 2 weeks; a subacute infection is one that lasts 2 to 6 weeks; and chronic infections are those that last longer than 6 weeks. Chronic osteomyelitis is generally defined as a bone infection that fails to respond to a normal course of antibiotic therapy. On histologic examination, chronic osteomyelitis is diagnosed when areas of necrotic bone are identified. Septic arthritis is defined as an infection of a joint by bacterial or fungal organisms. Bacterial arthritis is sometimes called pyogenic or suppurative arthritis. Reactive arthritis is more common than bacterial arthritis. It is a sterile, secondary inflammation of a joint with no identifiable infecting microorganisms within the synovial fluid. Commonly, reactive arthritis occurs after a systemic infection with a virus, but it can also develop after group A streptococcal infection. There are many classification systems for osteomyelitis based on the condition of the host, functional impairment caused by the disease, site of involvement, and extent of bone necrosis. For the emergency physician, the most practical way to classify osteomyelitis is as hematogenous osteomyelitis, which is more common, and osteomyelitis secondary to a contiguous focus of infection. Osteomyelitis from a contiguous focus is further subdivided on the basis of the presence or absence of vascular insufficiency. Vascular insufficiency is often secondary to trauma, surgery, or insertion of hardware into the bone, including a prosthetic joint. Recognition of the etiologic mechanism of osteomyelitis assists in the interpretation of diagnostic imaging examinations and helps guide management, including antibiotic therapy and surgical intervention. Septic arthritis usually results from hematogenous migration of bacteria into the joint, although it can be caused by direct inoculation of bacteria from trauma or joint aspiration or infected foreign material, such as a prosthesis. In some cases septic arthritis may occur concomitantly with osteomyelitis, with infection spreading from bone to joint, and vice versa.